Fluctuations between square-planar and tetrahedral coordination geometry with bis(2-benzimidazolyl)alkane ligands. Synthesis, spectroscopic properties and X-ray crystal structure of four representative examples

Abstract

Several new transition-metal(II) coordination compounds with the formula [M(L) 2(ClO 4) 2](sol) x (H 2O) y (in which L=bis(2-benzimidazolyl)ethane, abbreviated as dbz or bis(2-benzimidazolyl)propane, abbreviated as tbz, M=Cu(II), Ni(II); sol=MeOH, EtOH, 1-PropOH, ButOH, x=1–4, y=0–1) have been prepared and characterized structurally and spectroscopically. Four representative compounds, i.e. [Cu(dbz) 2](ClO 4) 2(C 2H 5OH) 2 ( 1), [Cu(tbz) 2](ClO 4) 2(C 3H 8O) ( 2), [Cu(tbz) 2](ClO 4) 2(C 3H 8O)(H 2O) ( 3) and [Ni(dbz) 2](ClO 4) 2(C 2H 5OH) 4 ( 4), were characterized structurally by X-ray diffraction. Structure 1 consists of a mononuclear Cu(II) ion surrounded by four nitrogen atoms of two dbz ligands, in a square planar geometry with trans angles of 180° and with one oxygen of a perchlorate molecule in an apical position with a distance of 2.9320(19) Å. Structures 2 and 3 both consist of a mononuclear Cu(II) ion surrounded by four nitrogens of two tbz ligands, in which the trans angles of 144.3(3) and 146.9(3)° for structure 2 and 138.9(4) and 142.0(4)° for structure 3, indicate quite a distorted square-planar geometry. The difference between both structures is that structure 3 has, in addition to a 1-propanol molecule, a water molecule in the lattice, whereas structure 2 has only a 1-propanol molecule in the lattice. Structure 4 consists of mononuclear Ni(II) ions surrounded by four nitrogens of two dbz ligands with trans angles of 176.8(2) and 175.8(2)°, indicative of an almost perfect square-planar geometry. In the far-IR an absorption is observed in compound 3 at 384 cm −1 which is absent in compounds 2 and 4 and which is ascribed to the librational mode of the water molecule present in the lattice.